Parts for your 2009 Honda Stream-Temperature sensors

2009 Honda Stream temperature sensors: what they do and how to look after them

Temperature sensors are absolutely fitted to the 2009 Honda Stream (RN6–RN9 series) and are essential for proper engine and climate operation. Honda’s factory service information and wiring diagrams for the RN6–RN9 models outline multiple temperature-related sensors: the engine coolant temperature (ECT) sensor for the ECU and fan control, an intake air temperature (IAT) sensor for fuel and ignition trim, an ambient air temperature sensor for the HVAC/outside temp display, and an automatic transmission fluid temperature sensor within the 5‑speed auto. These are documented in Honda’s Stream service manual, electrical troubleshooting manual, and parts catalogues for the R18A/R20A engines.

On a 2009 Honda Stream, temperature sensors quietly keep everything in the sweet spot. The ECT sensor tells the ECU how hot the engine is so it can adjust fuelling, ignition timing and idle speed, switch the radiator fans, and drive the temperature gauge. The IAT sensor helps fine‑tune mixture as intake temps change with weather and load. The ambient sensor feeds the climate control so the cabin temp stays comfortable. Together, they protect the engine, improve fuel economy, and keep the drive smooth.

As part of servicing, it’s smart to keep an eye on them. If the ECT or IAT drifts, the car may use more fuel, idle oddly, run the fans at the wrong time, or light the check engine lamp. A scan tool can show live ECT/IAT readings: cold starts should read close to ambient, then the ECT should warm to roughly the low‑90s °C under normal driving. Any jumpy or implausible values suggest a sensor or wiring issue.

• Typical symptoms: hard cold starts, rich running or poor economy, fluctuating temp gauge, fans stuck on or not coming on, rough idle, or AC performance that feels off.
• Basic care: keep connectors clean and dry, check for chafed looms under the bonnet, and fix coolant leaks quickly so dried coolant crystals don’t corrode plugs.
• Replacement tips: always let the engine cool, depressurise the cooling system, and use new O‑rings/seals. Refill with the correct Honda‑spec coolant and bleed air as per the service manual.

For the ECT sensor, it’s typically mounted near the thermostat housing, the IAT is in the intake duct or housing. Use quality parts, avoid thread sealants unless specified, and tighten only to the service‑manual spec. If in doubt, a quick diagnostic session with a scan tool will confirm sensor health before you spend on replacements.

How can someone tell if the coolant temperature sensor is failing on a 2009 Honda Stream?

Common giveaways include a cold start that’s too rich or too lean, a radiator fan that runs at odd times, a wandering temperature gauge, or a check engine light. With a scan tool, compare the ECT reading to the outside temperature on a true cold start, a big mismatch points to the sensor or its wiring.

After warm‑up, the ECT should rise smoothly without spikes. Any sudden dropouts, stuck readings, or obvious corrosion at the connector are good reasons to test and replace.

Does the cooling system need bleeding after replacing the ECT sensor?

Yes, because removing the ECT sensor can introduce air. Refill with the correct Honda coolant mix and bleed as per the service manual to prevent hot spots, heater issues, and false temperature readings. Running the engine with the heater on and watching for steady fan cycling helps confirm the system is free of air.

Where is the intake air temperature sensor on the 2009 Honda Stream?

On RN6–RN9 models it’s typically fitted in the intake duct or integrated near the intake manifold. Look for a small two‑wire sensor pushed into the duct with an O‑ring. If the airbox or intake has been modified, ensure the sensor is still positioned to read true incoming air, not heat‑soaked air from the engine bay.